1. Field of the Invention
This invention relates to a method and apparatus for treating shale gas waste water that includes dissolved chlorides and, more particularly, to a method and apparatus for producing a chloride-based product from a clean chloride solution obtained through a waste water treatment process.
2. Description of the Related Art
Purified water is used in many industries including the chemical, foodstuffs, electronics, power, medical and pharmaceutical industries, as well as for human consumption. Typically, prior to use in any one of these fields, the water is treated to reduce the level of contaminants to acceptable levels. These treatment techniques include disinfection, distillation, filtration, ion exchange, reverse osmosis, photooxidation, ozonation, and combinations thereof.
Various levels of purity may be required for different end uses. Water quality may be regulated by various government agencies and trade organizations including the U.S. Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA).
One field in which the treatment of water is necessary is in the natural gas extraction field. Extracting natural gas trapped in shale formations and other gas reservoirs often requires the use of hydraulic fracturing (also known as “fracing” or “well stimulation”). Fracing has been used safely and effectively for over sixty years. The goal of the fracing process is to create a pathway of man-made cracks in the rock that allow gas to flow from the shale into the wellbore. Without this technique, many natural gas reservoirs would not produce natural gas.
The fracing process is very water intensive, so that steps must be taken to protect groundwater. In very tight rock formations (i.e. rock formations in which gas cannot migrate through the formation naturally), a greater amount of water is used to stimulate the fractures and enhance gas flow. These formations require more water than a traditional shallow well.
The fracing of a shale well takes place after the well has reached a desired vertical and/or horizontal depth and can last for several days. Once well casing is cemented in place to protect the water aquifers and gas production zones, a charge is fired into the formation at the end of the wellbore. It perforates the steel casing, cement and shale formation to provide a pathway for the fresh water injection.
Fluids pumped under pressure act as a wedge to crack the rock during fracing operations. The fluid includes water, sand, and special-purpose additives that are injected into the wellbore. The additives are mixed in self-contained systems where fluids are not exposed to the environment. Some of the additives are commonly referred to as “slickers” or “slicker” chemicals.
Some additives include acids, such as hydrochloric acid or muriatic acid, which dissolve minerals and initiate cracks in the rocks, and anti-bacterial agents, such as glutaraldehyde, which eliminate bacteria in the water that produce corrosive by-products. Breakers, such as ammonium persulfate, that allow for a delayed break down of the gel are also used to thicken the water in order to suspend the sand. Corrosion inhibitors, such as n,n-dimethylformamide, are also used to prevent the corrosion of pipe.
Common additives also include crosslinking agents, such as borate salts, that maintain fluid viscosity as temperature increases, and gels, such as Guar gum or hydroxyethyl cellulose, that thicken the water in order to suspend the sand. Other common additives include chemicals for controlling iron content, such as citric acid, which prevent the precipitation of metal oxides, and potassium chloride that creates a brine carrier fluid.
Oxygen scavengers, such as ammonium bisulfate, are used to remove oxygen from the water to protect pipes from corrosion. Other common additives include pH adjusting agents, such as sodium or potassium carbonate, for maintaining the effectiveness of other components such as the crosslinking agents.
Other additives also include proppants, such as silica or quartz sand, which allows the fractures to remain open so that the gas can escape, and scale inhibitors, such as ethylene glycol, which prevent scale deposits in the pipe. Surfactants, such as isopropanol, are also used to increase the viscosity of the fracture fluid.
A significant portion of the fluid returns to the surface through the protective casing. It is highly monitored, collected and saved in tanks or lined pits on the well site for later transport to permitted disposal facilities. This returned fluid, called “flowback,” can pick up heavy salts and minerals.
Additional amounts of water used in the fracing process remain in the shale formation nearly a mile below the Earth. The remaining water returns slowly over time at the well site and is redirected into collection tanks where it is removed and treated.
The fracing process produces a waste water stream that is contaminated with multiple contaminants, namely oil/grease, soluble organics, heavy salts, minerals, trace metals, extremely high concentration of chlorides, and, optionally, radioactive nuclei. Since the need to protect ground water is great, the waste water must be treated to remove the contaminants so that the waste water does not contaminate the ground water.
Many methods for treating waste water are known. U.S. Patent Publication Nos. 2008/0116136 and 2009/0045135 disclose general methods for treating waste water. Other methods include methods for removing metals, particularly heavy metals, such as the method disclosed in U.S. Pat. Nos. 3,761,381, 4,157,942, 4,171,255, and 4,652,352.
U.S. Pat. No. 4,652,352 discloses a method for recovering heavy metals from dilute solutions. U.S. Pat. Nos. 3,761,381, 4,157,942 and 4,171,255 disclose methods for recovering heavy metals from aqueous solutions.
U.S. Pat. No. 6,214,233 discloses a method for treating a waste water stream that contains cyanide bearing compounds and heavy metals, such as copper, silver, nickel, and iron. The method utilizes a stripping solution to remove adsorbed metals from adsorption materials.
U.S. Pat. No. 5,770,090 discloses a method for treating a waste water stream that contains heavy metals, such as chromium, zinc, and copper. The method utilizes activated carbon as an adsorption material. The method also utilizes a stripping solution to remove the adsorbed metals from the adsorption material.
U.S. Pat. No. 3,973,987 discloses a water recycle treatment system. The system feeds treated water to a distillation unit to precipitate the metals and salts in sludge and also forms a water vapor output.
Other methods for treating waste water are directed to methods and apparatus for removing organic compounds from the water. U.S. Pat. No. 4,929,359 discloses a method for treating highly concentrated and toxic petroleum-based and synthetic fuels waste waters, such as oil shale retort water using electrolysis. The treatment is performed in a reactor that contains polyurethane foams.
U.S. Pat. No. 7,441,665 discloses a water purification cartridge. The water purification cartridge includes porous diatomaceous earthen ceramic water filters or carbon filters packed with granulated activated carbon or block.
U.S. Pat. No. 6,709,585 discloses a waste water purification system. The system includes a tank-filter for performing a pre-treatment step. The tank includes a flocculant that is uniformly mixed with an agitator. The pretreated water is directed to a collecting tank for clarification. The clarified, pre-treated water is directed through a safety filter to a battery of activated carbon columns for treatment. In another embodiment, a polypropylene bag filter that includes diatomaceous earth is used to pre-treat the waste water.
Many waste water treatment methods utilize diatomaceous earth or activated carbon. U.S. Pat. No. 4,568,463 discloses a method and apparatus for purifying aqueous solutions. A diatomaceous earth coarse filter is used to pre-treat the solution. An activated charcoal column is used to finish the process. Optionally, chloride is utilized to kill microorganisms.
U.S. Pat. No. 4,454,044 discloses a water treatment process. The process involves contacting water with a relatively small amount of diatomaceous earth particles or activated carbon particles to adsorb impurities. After contact with the particles, the water is passed through a filter.
U.S. Pat. No. RE 35,871 discloses a water reclamation system for car washes. The system uses a diatomaceous earth filter for removing particulates and a carbon filter for removing organic contaminants. The diatomaceous earth filter removes particles of dirt, oil, and rust. The carbon filter includes activated charcoal that removes dissolved organic materials, such as oil and surfactants. The system also utilizes chloride or ozone to kill algae.
Other methods for treating water are directed to desalination methods. A publication entitled “Capacitive Deionization Technology™: An alternative desalination solution” by T. J. Welgemoed and C. F. Schutte, Desalination 183 (2005) at 327-40, discloses that possible desalination techniques for brackish water include reverse osmosis, electrodialysis, and a low-pressure non-membrane desalination process that is identified by the trademark Capacitive Deionization Technology™.
A publication entitled “Desalination technology could clean up wastewater from coal-bed methane production” by K. Christen, Environmental Science & Technology Online News, Jan. 11, 2006, accessed http://pubs.acs.org on Oct. 28, 2008, discloses that such technologies can be used in the treatment of waste water from coal-bed methane production.
However, none of the above described water treatment methods are effective in treating the waste water streams that include the combination of oil and grease, soluble organics, trace metals, and extremely high concentration of chlorides that are produced in “fracing” operations in the extraction of natural gas from shale formations. Accordingly, an improved waste water treatment is needed.